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United States Patent |
5,676,734
|
Oberndorfer
,   et al.
|
October 14, 1997
|
Method of treating fine ore
Abstract
In a process for treating fine ore, the fine ore is dried by aid of a hot
drying gas flowing around the ore particles of the fine ore, the drying
gas, after having flown around the ore particles, is purified while
releasing entrained dust ore particles and the dust ore particles are
collected and admixed to the dried fine ore. In order to avoid process
disturbances in the further processing of fine ore due to excessive
portions of dust ore particles present within the fine ore,
drying is effected in the whirl-bed, i.e., fluidized-bed method under
simultaneous wind-screening of the fine ore, wherein
the drying gas is passed through the fine ore under formation of a whirl
bed and
the speed of the drying gas is fixed at a rate at which entraining of dust
ore particles having dimensions below a predetermined dimension is
effected, and
that the dust ore particles entrained by the drying gas are separated,
collected and admixed to the dried fine ore in dosed amounts.
Inventors:
|
Oberndorfer; Ernst (Leonding, AT);
Tessmer; Gero (Linz, AT);
Weidinger; Rudolf (Linz, AT);
Whipp, Jr.; Roy Hubert (Miami, FL)
|
Assignee:
|
Voest-Alpine Industrieanlagenbau GmbH (AT);
Brifer International Ltd. (BB)
|
Appl. No.:
|
408485 |
Filed:
|
March 22, 1995 |
Foreign Application Priority Data
Current U.S. Class: |
75/754; 75/450; 75/961; 266/172 |
Intern'l Class: |
C22B 001/10 |
Field of Search: |
75/450,754,961
266/172
|
References Cited
U.S. Patent Documents
3817696 | Jun., 1974 | Hereth | 432/15.
|
5082251 | Jan., 1992 | Whipp | 266/142.
|
Foreign Patent Documents |
0010627 | May., 1980 | EP.
| |
0149865 | Jul., 1985 | EP.
| |
0571358 | Nov., 1993 | EP.
| |
906V | Oct., 1950 | DE.
| |
1458755 | Mar., 1969 | DE.
| |
1224933 | Sep., 1972 | DE.
| |
2434917 | Feb., 1975 | DE.
| |
318904 | Mar., 1957 | CH.
| |
Primary Examiner: Andrews; Melvyn
Attorney, Agent or Firm: Ostrolenk, Faber, Gerb & Soffen, LLP
Claims
What we claim is:
1. In a process for treating fine ore in need of being dried and formed of
ore particles including dust ore particles, by providing a hot drying gas,
supplying said fine ore and drying said fine ore by aid of said hot drying
gas flowing at a speed around said ore particles so as to obtain dried
fine ore, purifying said drying gas, after having flown around said ore
particles, so as to release entrained dust ore particles, collecting said
released entrained dust ore particles and admixing said released entrained
dust ore particles to said dried fine ore, the improvement comprising the
steps of:
drying of said fine ore by aid of said hot drying gas in a fluidized bed so
as to produce dried fine ore;
wind-screening said fine ore, by passing said hot drying gas through said
fine ore under formation of said fluidized bed and fixing the speed of
said hot drying gas at a rate so as to effect entraining in said hot
drying gas of said dust ore particles having grain dimensions below a
selected dimension;
separating from said dried fine ore said dust ore particles having grain
dimensions below said selected dimension and entrained by said drying gas;
collecting said dust ore particles separated from said dried fine ore to
produce separated and collected dust ore particles; and
admixing said separated and collected dust ore particles to said dried fine
ore in dosed amounts.
2. A process as set forth in claim 1, wherein said dried fine ore, after
having left said fluidized bed, is collected and mixed in dosed amounts
with said separated and collected dust ore particles supplied in dosed
amounts.
3. A process as set forth in claim 1, wherein mixing of said dried fine ore
with said separated and collected dust ore particles is effected at a
quantitative ratio ranging from 90:10 to 70:30.
4. A process as set forth in claim 1, wherein mixing of said dried fine ore
with said separated and collected dust ore particles is effected at a
quantitative ratio ranging from 80:20 to 85:15.
5. A process as set forth in claim 1, wherein admixing of said separated
and collected dust ore particles to said dried fine ore is effected while
maintaining a constant quantitative ratio of separated and collected dust
ore particles to dried fine ore.
6. A process as set forth in claim 1, wherein admixing of said separated
and collected dust ore particles to said dried fine ore is effected while
maintaining a constant overall amount of separated and collected dust
being admixed per time unit.
7. A process as set forth in claim 1, wherein the speed of said drying gas
is fixed at a rate at which dust ore particles having grain dimensions
smaller than 200 .mu.m are entrained by said drying gas.
8. A process as set forth in claim 1, wherein the speed of said drying gas
is fixed at a rate at which dust ore particles having grain, dimensions
smaller than 150 .mu.m are entrained by said drying gas.
9. A process for treating fine ore in need of being dried and formed of ore
particles comprising the steps of:
providing a hot drying gas;
supplying fine ore;
drying said fine ore by aid of said hot drying gas flowing at a speed
around said ore particles in a fluidized bed so as to obtain dried fine
ore;
wind-screening said fine ore by passing said hot drying gas through said
fine ore under formation of a fluidized bed;
fixing the speed of said hot drying gas at a rate so as to entrain in said
hot drying gas dust ore particles having grain dimensions below a selected
dimension;
separating and collecting said dust ore particles from said drying gas to
produce separated and collected dust ore particles; and
admixing said separated and collected dust ore particles with said dried
fine ore in dosed amounts.
10. A process as set forth in claim 9, wherein said dried fine ore, after
having left said fluidized bed, is collected and mixed in dosed amounts
with said separated and collected dust ore particles supplied in dosed
amounts.
11. A process as set forth in claim 9, wherein mixing of said dried fine
ore with said separated and collected dust ore particles is effected at a
quantitative ratio ranging from 90:10 to 70:30.
12. A process as set forth in claim 9, wherein mixing of said dried fine
ore with said separated and collected dust ore particles is effected at a
quantitative ratio ranging from 80:20 to 85:15.
13. A process as set forth in claim 9, wherein admixing of said separated
and collected dust ore particles to said dried fine ore is effected while
maintaining a constant quantitative ratio of separated and collected dust
ore to dried fine ore.
14. A process as set forth in claim 9, wherein admixing of said separated
and collected dust ore particles to said dried fine ore is effected while
maintaining a constant overall amount of separated and collected dust ore
particles being admixed per time unit.
15. A process as set forth in claim 9, wherein the speed of said drying gas
is fixed at a rate at which dust ore particles having grain dimensions
smaller than 200 .mu.m are entrained by said drying gas.
16. A process as set forth in claim 9, wherein the speed of said drying gas
is fixed at a rate at which dust ore particles having grain dimensions
smaller than 150 .mu.m are entrained by said drying gas.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for treating fine ore, wherein the fine
ore is dried by aid of a hot drying gas flowing around the ore particles
of the fine ore, the drying gas, after having flown around the ore
particles, is purified while releasing entrained dust ore particles and
the dust ore particles are collected and admixed to the dried fine ore, as
well as an arrangement for carrying out the process.
2. Description of the Related Art
A process of this type is known from U.S. Pat. No. 5,082,251. There, drying
of the fine ore is effected in a rotating drum type drier.
The further processing of fine ore, such as the direct reduction of fine
ore, involves difficulties if dust ore particles are contained in the fine
ore in excessive amounts, in particular, dust ore particles having
dimensions smaller than 150 .mu.m. An excessive portion of such dust ore
particles in the fine ore is likely to give rise to serious process
disturbances in further processing caused, for instance, by obstructed
ducts, cyclones or by the formation of deposits in reactor vessels. Such
disturbances also may arise if the portion of dust ore particles is
acceptable as a whole, yet the distribution of the dust ore particles
within the fine ore strongly varies. Consequently, maximum contents of
dust ore particles may occur, lying considerably above the dust ore
particle portion to be coped with without any disturbances; such maximum
content portions may amount up to 50%.
From EP-A-0 149 865 it is known to subject sulfidic ores to whirl bed
drying. With this known process, the total amount of solids is supplied to
gas purification together with the exit gas from whirl bed drying through
a duct, the solids separated in purification being admixed to the
previously separated solids without considering their grain dimensions.
Thus, no wind-screening is provided here.
From CH-B-318.904 it is known to finely pulverize ore oxides and to subject
the incurring powdery stock to wind-screening by using reducing gas for
wind-screening. The coarser iron powder retained in wind-screening is
returned to the pulverization procedure such that uniformly fine powder
ore particles exclusively will be available to the reduction of the ore.
DE-A-1 458 755 relates to a process for controlling the grain size
distribution and the fine grain concentration in whirl-layer reaction
zones. There, a fine grain concentration ranging between 5 and 60% by
weight is adjusted in the whirl layer by withdrawing fine grains of a
predetermined grain size range from the whirl layer and returning them
back into the whirl layer in circulation in given amounts. What is
important there is to counteract the enrichment of the amount of fine
grains contained in the whirl-layer reaction zone due to the formation of
new fine grains caused by abrasion in that zone. Hence, the process does
not deal with the treatment of fine ore, but with a process taking place
during its reduction.
SUMMARY OF THE INVENTION
The present invention avoids process disturbances in the further processing
of fine ore due to excessive portions of dust ore particles present within
the fine ore. In particular, strongly fluctuating portions of dust ore
particles are to be avoided and an approximately constant quantitative
portion of dust ore particles whose grain dimensions are less than a
predetermined grain size limit is to be present at any time in the fine
ore subjected to further processing, wherein it is particularly suitable
if dumping of dust ore particles can be avoided if at all possible. In
accordance with the invention,
drying is effected in the whirl-bed, i.e., fluidized-bed method under
simultaneous wind-screening of the fine ore, wherein
the drying gas is passed through the fine ore under formation of a whirl
bed and
the speed of the drying gas is fixed at a rate at which entraining of dust
ore particles having dimensions below a predetermined dimension is
effected, and
that the dust ore particles entrained by the drying gas are separated,
collected and admixed to the dried fine ore in dosed amounts.
By collecting dust ore particles, it is feasible to block and balance out a
temporarily present excess of dust ore particles, wherein the dust ore
particles collecting are admixed to the direct reduction process in case
fewer dust ore particles incur in drying than are consistent with further
processing, or in case fewer dust ore particles incur than are intended to
be supplied to further processing, such as a direct reduction process. The
balance thus obtained allows for minimization, or even total avoidance, of
portions of dust ore particles to be dumped.
According to the invention, advantageously also the dried fine ore, after
having left the whirl bed, is collected and is mixed in dosed amounts with
the dust ore particles fed in dosed amounts. Thereby, a uniform flow of
dried fine ore is made available for admixture to the dried dust ore
particles.
Suitably, mixing of the dried fine ore with the dust ore particles is
effected at a quantitative ratio ranging from 90:10 to 70:30, preferably
ranging from 80:20 to 85:15.
Advantageously, mixing of the dried fine ore with the dust ore particles is
effected while observing a constant predetermined quantitative ratio,
mixing of the dried fine ore with the dust ore particles suitably being
effected while observing a constant overall amount per time unit.
It has been proved to be particularly suitable with a direct reduction
process like that described, for instance, in U.S. Pat. No. 5,082,251, if
the speed of the drying gas is fixed at a rate at which dust ore particles
whose grain dimensions are smaller than 200 .mu.m, preferably smaller than
150 .mu.m, are entrained.
An arrangement for carrying out the process according to the invention is
characterized by the following characteristic features:
a fine-ore whirl bed drier comprising a drying-gas feeder,
a drying-gas purification means arranged to follow said whirl bed drier and
comprising
a separating means separating from the drying gas dust ore particles
entrained by the drying gas,
a collecting vessel receiving the separated dust ore particles, and
a mixing means for mixing the dried fine ore with the dust ore particles
separated from the drying gas to a predetermined quantitative ratio.
Advantageously, a collecting vessel receiving the dried fine ore is
arranged to follow the whirl bed drier.
Suitably, a proportioning belt weigher for the dust ore particles is
arranged to follow the collecting vessel receiving the separated dust ore
particles, wherein, furthermore, a proportioning belt weigher for the
dried fine ore advantageously likewise is arranged to follow the
collecting vessel receiving the dried fine ore.
The drying gas advantageously is formed by burning a gas, wherefor the
whirl bed drier suitably is equipped with a gas firing, preferably a
natural gas firing, intended to produce a drying gas.
BRIEF DESCRIPTION OF THE DRAWING
In the following, the invention will be explained in more detail by way of
an exemplary embodiment illustrated in the drawing, the drawing
representing a process diagram according to a preferred embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The arrangement according to the invention comprises a storage tank 1 for
fine ore 2, which, for instance, is used for the production of sponge iron
by direct reduction with reducing gas. From the storage tank 1, the fine
ore 2, via a proportioning belt 4 equipped with scales 3, gets into a
whirl bed drier 5 provided with a gas firing 6 for producing a drying gas
7. The gas firing 6 advantageously is operated with natural gas 8. The
drying gas 7 formed at the combustion of natural gas 8 is fed into the
interior 11 of the whirl bed drier 5 through a distribution grid 10
provided with a plurality of tuyeres 9, the drying gas 7 emerging from the
tuyeres of the distribution grid 10 at a predetermined rate. The rate of
the drying gas 7 can be adjusted to the desired value by control of the
gas firing 6.
On the upper end of the whirl bed drier 5, the drying gas 7 is fed, via a
discharge duct 12, to a drying-gas purification means 13, which is
designed as a cyclone separator. In the cyclone separator 13, the
separation of dust ore particles 14 entrained with the drying gas 7 takes
place, which dust ore particles are conveyed from the cyclone separator 13
to a collecting vessel 16 via a conveying duct 15.
The fine ore 17 dried in the whirl bed drier 5 and freed from dust ore
particles 14, via a conveying duct 18, likewise reaches a collecting
vessel 19. From there, the dried fine ore is supplied, via a proportioning
belt weigher 20, to a mixing means 21 for mixing the dried fine ore 17
with a predetermined portion of dust ore particles 14 likewise supplied to
the mixing means 21 via a proportioning belt weigher 22. The mixing means
21 is designed as a conveying belt to be fed from the two proportioning
belt weighers 20, 22.
The arrangement functions in the following manner:
In the whirl bed drier 5, a whirl bed forms under supply of drying gas 7
fed through the tuyeres 9 of the distribution grid 10 and ascending at a
predetermined flow rate in the interior 11 of the whirl bed drier 5, fine
particles, such as dust ore particles 14, having grain dimensions below a
predetermined grain size limit being entrained by the drying gas 14. The
grain size limit is a function of the flow rate of the drying gas 14. The
flow rate of the drying gas 14 suitably is chosen such that all of the
dust ore particles 14 having dimensions below approximately 150 .mu.m are
discharged along with the drying gas. These dust ore particles 14 are
separated in the cyclone separator 13 and are supplied to the collecting
vessel 16.
By aid of the two proportioning belt weighers 20, 22, the supply of dried
fine ore 17 and dried dust ore particles 14 is adjusted in manner that a
(preferred) quantitative ratio of dried fine ore 17 to dried dust ore
particles 14 ranging from about 80:20 to 85:15 is obtained, the overall
amount of the fine ore mixture 23 formed of dried fine ore 17 and of dust
ore particles 14 being kept constant.
If an excessive amount of dust ore particles 14 incurs, a portion of the
same may be conducted to a dumping ground or supplied to a further
collecting vessel 25 for intermediate storage through a branch duct 24,
the intermediately-stored dust ore particles 14 being admixable together
with the dried fine ore 17 at a later point of time in case the unscreened
fine ore 2 supplied to the whirl bed drier 5 contains a smaller amount of
dust ore particles 14, as is indicated by broken line 26.
The fine ore mixture 23 leaving the conveying belt 21 at a constant amount
and a constant quantitative ratio of dried fine ore 17 to dried dust ore
particles 14 per time unit subsequently is supplied to a direct reduction
plant according to U.S. Pat. No. 5,082,251 or EP-A-0 571 358 or EP-B-0 010
627 for the purpose of producing sponge iron.
The process according to the invention enables the progression of such
direct reduction processes without any problem, because process
disturbances that might be caused on account of a sudden excessive amount
of dust ore particles 14 are safely avoided.
In Table 1 below, fine ores I to IV having different contents of dust ore
particles (grain dimensions below 150 .mu.m) are listed:
TABLE 1
______________________________________
Fine Ore Dust Ore Particles %
______________________________________
I 49
II 35
III 25
IV 18
______________________________________
These fine ores were used in the whirl bed drier 5 in the amounts (t/h)
indicated in Table 2 for the production of 70 t/h of briquetted sponge
iron (Table 2). The water content separated by the drying gas 7 likewise
is indicated in Table 2. The dust ore particles 14 (grain dimension
smaller than 150 .mu.m) also indicated in Table 2 were discharged by the
drying gas 7 and separated in the cyclone separator 13.
TABLE 2
______________________________________
Fine Ore
Charge t/h Water Content t/h
Dust Ore Particles t/h
______________________________________
I 168 9.80 73.1
II 137 8.05 44.1
III 122 7.35 29.4
IV 113 6.65 21.0
______________________________________
From each of the fine ores I to IV, 86.1 t/h dried fine ore 17 freed from
dust ore particles 14 were mixed together with 18.9 t/h dust particles 14
each (fine ore mixture 23, amount 105 t/h) and subjected to a direct
reduction process as described in EP-A-A0 571 358:
______________________________________
Carbon supply 0.7 t/h
Oxygen separated
26.6 t/h
Losses on ignition
4.2 t/h
Dust separated 2.1 t/h
______________________________________
72.1 t/h of sponge iron were produced. The losses during briquetting were
2.1 t/h such that sponge iron briquets incurred in an amount of 70 t/h.
Although the present invention has been described in relation to particular
embodiments thereof, many other variations and modifications and other
uses will become apparent to those skilled in the art. Therefore, the
present invention is to be limited not by the specific disclosure herein,
but only by the appended claims.
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